Exotic Stars: Extreme Physics

Question 1

How do exotic stars form?

Answer 1

Nuclear fuel runs out
Thermal pressure fails
Gravitational collapse to smaller size
New equilibrium between gravity and quantum degeneracy pressure

Question 2

What kind of stars are exotic?

Answer 2

White dwarf stars

Neutron stars

Question 3

Why are exotic stars useful?

Answer 3

Strong tests of quantum mechanics, special and general relativity

Question 4

Type 1a supernova

Answer 4

When a white dwarf has a companion and explodes

Question 5

How much energy is released in a type 1a supernova

Answer 5

Suns lifelong output

Question 6

How hot is a type 1a supernova

Answer 6

100 Tsun

Question 7

How bright is a type 1a supernova

Answer 7

5 billion x Lsun (about a galaxy)

Question 8

Mysteries of the type 1a supernova

Answer 8

Single/double degenerate progenitors

How does the explosion happen in detail

Question 9

Type 1a supernovae - recent supercomputer simulations

Answer 9

Ignition not from gravitational collapse?
Pressure and temp slowly increase until Tcore reaches fusion temp right before M reaches Mch
Small flame bubble starts near centre
OR
Nuclear burn (flame starts from carbon fusion,oxygen fusion stars later, subsonic deflagration -> supersonic detonation)

Question 10

Type II supernova

Answer 10

Stars mass > 8-10 sun
Onion layered fusion with Inert nickel iron core (WD) supported by electron degeneracy pressure
Nickel iron ash deposited until core mass reaches Mch and collapses
Electrons squish until they fuse with protons to make neutrons
Outer shell free falls in

Question 11

Type II supernova what is the collapse halted by? What happens after?

Answer 11

Repulsive strong force and neutron degeneracy
There’s a bounce
Them an outward moving shockwaves
Only sun’s lifetime output involved in visible blast which leaves behind rest

Question 12

Mysteries of Type II supernova

Answer 12

Nature of short range nuclear forces
How burst of neutrinos converts 1% of energy to produce shock wave that causes SN explosion
Hypernovae, gamma ray bursts etc

Question 13

What are neutron stars?

Answer 13

Giant atomic nucleus
Strong gravitational field
Strong magnetic field
Rapid rotation - pulsar

Question 14

How do you get from white dwarf to neutron star

Answer 14

me -> mn ~ mp

Mu=2 -> mu=1

Question 15

Chandrasekhar limit

Answer 15

1) Emax = cp
2) p max = cNe^1/3h/2R
3) Pmax = NkT/V = N/V (2Emax/3)
4) Pc = Pmax

Question 16

Inert white dwarf

Answer 16

Core held up by electron degeneracy pressure
H burning she’ll deposits ash, growing core
Wind from burning expels outer layers - red giant - planetary nebula
Wind is fast enough that M doesn’t exceed Mch

Question 17

White dwarf supernova

Answer 17

WD core orbiting companion star
H pulled onto WD by tidal forces
M slowly increases until M=Mch
Supernova 
Nuclei free fall until gravity
Temp up
Flash nuclear burn

Question 18

Death of a high mass star

Answer 18

1) more massive core - hotter core

2) loss of mass during giant phase can’t keep mass less than Mch

Question 19

Parts of a supernova

Answer 19

Collapse
Bounce
Explosion

Question 20

Supernova - collapse

Answer 20

Core - gas of e and Fe, v->c
Gravitational collapse
Beta decay happens (n formed)

Question 21

Supernova - bounce

Answer 21

Repulsive nuclear force at short distance

Neutron degeneracy pressure

Question 22

Supernova - explosion

Answer 22

Energy of stellar mass is only 10^44J

Neutrinos carry away almost all the 10^46J of gravitational PE

Question 23

Neutron stars

Answer 23

All nuclei have same density
Strong nuclear force has hard core of repulsion (not understood)
Stabilized by gravity (against repulsive force)

Question 24

Neutron stars - strong gravitational field

Answer 24

Can use Newtonian gravity as rough approx

Question 25

Neutron stars - strong magnetic field

Answer 25

Plasma is highly conducting
B lines frozen into plasma
Plasma in tube of B lines always remains as plasma moves
In NS same number of B lines through tiny area
Charged particles spiral around them
-photons split in two
-vacuum itself is polarized

Question 26

Neutron stars - rapid rotation

Answer 26

Conservation of angular momentum
Changing B field is changing E field
Pulsars lol